The requirements on a telecommunication system regarding availability are very high compared to other comparable systems. As the traffic, such as phone calls and data traffic, through the telecommunication system increases the power consumption of the telecommunication system increases. New technologies also make it possible to reduce the size of hardware. This reduction in size results in a higher power consumption in different parts of the telecommunication system since more hardware can be fitted in the different parts.
This means that there is a need for supplying more power to different parts in the telecommunication system. Power is often supplied to the different parts in the telecommunication system through a power cable from a power source to a part in the telecommunication system that requires power. There is, however, an upper limit for how much power that can be supplied through the cable from the power source to the part that needs power. The amount of power that can be supplied through the power cable may for instance be limited by the length of the power cable. Another factor that limits the amount of power that can be supplied through the power cable is the cross-sectional area of the respective conductors in the power cable. If there is a fuse in connection with the power cable this fuse will also limit the amount of power that can be supplied through the power cable.
One solution to this problem is to supply power from the power source to the part that requires power via several power cables in parallel. When using several power cables more power can be delivered to the part in the telecommunication system that requires power.
There is, however, at least one problem associated with this solution, namely the problem of matching the loads supplied by the respective cables in order to utilize as much of the power that is supplied trough one power cable as possible. If for instance 800 W could be supplied through one power cable, then it would be an advantage to for instance supply power to four loads needing 200 W each through this power cable, since this would result in that all the power that could be fed through this cable is utilized. Matching of the loads to fully take advantage of the power supply capacity of the different power cables is however often hard to perform in reality.
One possible solution to avoid the need for load matching on the separate power cables is to connect several power cables to a common fed line 30 as illustrated in FIG. 1a. FIG. 1a illustrates a power source 31 that supplies power to a power consuming unit 32 via three separate power cables 33, 34, and 35, where the three separate power cables are connected to the common fed line 30. This solution doesn't require matching of loads (not shown) in the power consuming unit 32 since all the loads are supplied via the common fed line 30.
A problem with this solution is however that in a case of a short circuit in the power consuming unit 32 there will be a much higher fault current from the power source 31 than in a case with a short circuit on a single power cable. This is because the power cables 33, 34, 35 are connected in parallel between the power source 31 and the power consuming unit 32, which results in a lower resistance between the power source 31 and the power consuming unit 32. The high fault current will result in a high voltage drop at the power source 31 which results in that other power consuming units (not shown) that are connected to the power source 31 will stop working or malfunction.
A solution for reducing the fault current and thereby the voltage drop in case of a short circuit in the arrangement according to FIG. 1 is to connect resistors (not shown) in series with the power cables 33, 34 and 35. This will however result in excessive heat generation.
Another solution is to arrange a hold up capacitor (not shown) in each power consuming unit that is connected to the power source 31. These hold up capacitors will power the different power consuming units in case of a voltage drop at the power source until a fuse trip, which will stop the voltage drop. However, in case of high fault current resulting in a high and fast voltage drop large hold up capacitors in the power consuming units are required. Large hold up capacitors in the power consuming units are also required if the power consumption of the power consuming units are high. This since the hold capacitors must be able to power the power consuming units for a considerable amount of time.
There is therefore a need for an improved solution for increasing the amount of power that can be supplied from a power source to a power consuming unit, which solution solves or at least mitigates at least one of the above mentioned problems.